Conventionally, there has been known a technique of purifying exhaust gas discharged from a diesel engine by setting in an exhaust passage of the diesel engine a case (hereinafter, refer to as DPF case) which is inward provided with a diesel particulate filter, and a case (hereinafter, refer to as SCR case) which is inward provided with an urea selective reduction type catalyst, as an exhaust gas purification device (an exhaust gas post-treatment device), and introducing exhaust gas to the DPF case and the SCR case (refer, for example, to Patent Documents 1 to 3). Further, a combine harvester has been conventionally structured such as to cut unreaped grain straws in a farm field by a reaping blade device, convey the reaped grain straws to a threshing device by a grain straw conveyance device to thresh, and collect the grains in a cereal grain tank, and is structured such that an engine is mounted to a travel machine body, the DPF case is arranged in a transversely directing posture on an upper surface side of the engine, and the exhaust gas is discharged from the engine toward the DPF case (refer, for example, to Patent Document 4).